This section is intended to introduce the reader to various aspects of art, which may be related to various aspects of the present invention that are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Projection televisions create video images by varying the color and shade of projected light. One example of a projection television system is a liquid crystal display (“LCD”) projection television. Another example of a projection television system is a Digital Light Processing (“DLP”) system. DLP systems employ an optical semiconductor, known as a Digital Micromirror Device (“DMD”) to project video onto a screen. DMDs typically contain an array of at least one million or more microscopic mirrors mounted on microscopic hinges. Each of these mirrors is associated with a point on the screen, known as a pixel. By varying the amount of light that is reflected off each of these mirrors, it is possible to project video images onto the screen. However, the lenses and mirrors needed to project video onto a screen results in distortion of the final image. Geometric distortion can be caused by projecting an image on a non-planar wall or at an angle. Geometric distortion can also occur in a cascade of lenses and mirrors used in the optical path of light-engine-based televisions.
Conventionally, a pixel-based form of electronic geometry correction is used. In this form, the pixel data itself is manipulated via resampling to achieve the desired geometric correction. The pixels are configured to project a corrected image with error relative to an idealized grid. In other words, along the lines of the idealized grid, the image should appear to be linear along a vertical and horizontal axis. However, due to distortions in the mirrors that reflect light to form images, the lenses used to project these same images, and other design factors, the uncorrected images may appear to be distorted and be curved along the vertical and horizontal axis.
One method of correction is referred to herein as the “offset method.” The offset method attempts to correct for arbitrary or near-arbitrary forms of distortion in a computation-intensive manner. A large number of offset coefficients are employed to compute a corrected image position for pixels relative to an expected position at which pixels would be displayed. The expected position, which may be determined by actual measurement data, may be attributable to a large number of physical factors relating to the design of the system.
In application of the offset method, the display area is divided into a fine grid and horizontal and vertical offset coefficients are specified at each of the grid points. Because it employs a large number of coefficients, response time to changes in system parameters may be relatively slow because of the coefficient transfer time required to manifest the changes. The offset method also typically requires smoothing to reduce the visibility of warping transitions between grid points.
A second method of electronic geometry correction employs coefficients that describe a high-order polynomial in horizontal and vertical directions. This method, which is referred to herein as the “polynomial method,” reduces the number of coefficients required to specify a particular geometric correction and provides inherently smooth transitions of warping on the screen. However, it is difficult to calculate the coefficients required to correct a particular arbitrary distortion and it requires sophisticated hardware to implement the actual correction to the pixel data. Also, this method employs fewer grid points and is, accordingly, does not allow as fine a correction capability as the offset method described above. A simpler method that would not require so much hardware, memory, and computing power while still providing an acceptable level of distortion correction is desirable.